(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "The Cambridge Natural History"

x                      FROM MlOHf^CrS TO ^QTOHIFPi/S                2.
size   than    AnnJiithemum,  to   be   considered   immediately.      1
odontoid process of the axis is jtisfc beginning to assume t
characteristic spout-like shape of that of the existing Horse a
many modern Ungulates. The median digit of both fore- a
hind-limbs has become greatly enlarged as compared with 1
corresponding digit of earlier forms.
It Is held, however, that AnoJiitherium is not on the dir
line of descent either In America or In Europe, In both of wh:
It occurs. Its teeth are in some respects less Horse-like than
some of the more ancient genera, to which the converse would
expected on the descent theory. Its hoofs are much elonga-
and flattened, a mark of specialisation and not appropriate
a creature holding an intermediate position In the equine ser.
Both the American (A. e^'uinuni) and the European species •
aitrefzease) are of very large size, larger than its successors,, e
sueli " nltemations in bulk are unlikely."
The genus Desmatt-ppHS of Professor Scott1 fills in the {
bet\Teeii J&Koliipp'US and frotoh-ipp'us. The molars and premol
are brachyodont, but there Is a thin deposit of cement In
tooth valleys, leading towards the more complete filling of tl~
valleys with cement, which Is found in Protohipp-us. This ge
of Horses, of which there Is at present but one species, D. crenid
was three-toed, and " the lateral digits, so far as can he judged
fragmentary remains, were still fairly developed, and thoi
nrach more reduced than in Miohippus, appear to he soxnew
less so than In JProtoJiippus**
To recapitulate, the following is the probable series of eqii3
in America—JMTesohippvis, Miohippus, Desmatipjpus, ProtoJiippu
The development of the limbs of the Horse shows a u
interesting series of stages, which, correspond in part to
ancestral forms which palaeontology seems to prove to be
line of the descent of our existing Equidae. This matter
recently been elucidated by Professor Ewart, who details
following facts and comparisons:—
In the youngest embryo (about 20 mm. in length)
humeros is somewhat curved, and considerably longer than
radius and carpus taken together. The first-named bom
shorter in the adult, and the proportions of that bone in
young as well as its curvature are suggestive of that anc
1 Trans. American Phil. Soc. acviii. 1896, p. 55.